Why is there a feeling of concern for the country and the people in Du Fu's poems?

This is a big question. If you explain it in detail, you can write a long paper. Let’s talk about it briefly here.

Most of Du Fu's early poems (before the age of 40) wrote about the majestic mountains and rivers, expressing his own emotions. Starting from the tenth year of Chang'an, his poems began to turn to the common people. "The Troops and Chariots" is his first-hand poem describing the common people. In "From Beijing to Fengxian County, Five Hundred Words of Ode to Bad Things" gradually formed his poem " The style of "Depressed and Melancholy" and "Concerned about the country and the people", later poems including "Officials trapped in thieves", poems written during the period of wandering in the southwest, etc. all paid attention to the common people, but they could not let go of the rulers, so they had some contradictions in their hearts.